fast-json-stable-stringify 2.1.0: fast-json-stable-stringify

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify fast-json-stable-stringify in pkg:npm/fast-json-stable-stringify@2.1.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/fast-json-stable-stringify@2.1.0
Demonstrate these symbols/APIs:
  - fast-json-stable-stringify
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

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{
  "name": "sample-fast-json-stable-stringify",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-fast-json-stable-stringify",
      "version": "1.0.0",
      "dependencies": {
        "fast-json-stable-stringify": "2.1.0"
      }
    },
    "node_modules/fast-json-stable-stringify": {
      "version": "2.1.0",
      "resolved": "https://registry.npmjs.org/fast-json-stable-stringify/-/fast-json-stable-stringify-2.1.0.tgz",
      "integrity": "sha512-lhd/wF+Lk98HZoTCtlVraHtfh5XYijIjalXck7saUtuanSDyLMxnHhSXEDJqHxD7msR8D0uCmqlkwjCV8xvwHw==",
      "license": "MIT"
    }
  }
}

{
  "name": "sample-fast-json-stable-stringify",
  "version": "1.0.0",
  "private": true,
  "dependencies": {
    "fast-json-stable-stringify": "2.1.0"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify fast-json-stable-stringify in pkg:npm/fast-json-stable-stringify@2.1.0",
  "kind": "HOW",
  "packages": [
    "pkg:npm/fast-json-stable-stringify@2.1.0"
  ],
  "symbols": [
    "fast-json-stable-stringify"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

const assert = require('node:assert/strict');
const stringify = require('fast-json-stable-stringify');

// 1. fast-json-stable-stringify serializes objects with keys sorted deterministically in lexicographical order
{
  const obj1 = { c: 8, b: 2, a: 1 };
  const obj2 = { a: 1, c: 8, b: 2 };
  assert.equal(stringify(obj1), '{"a":1,"b":2,"c":8}');
  assert.equal(stringify(obj1), stringify(obj2));
}

// 2. fast-json-stable-stringify recursively sorts nested object keys while preserving array element order
{
  const complex = {
    z: [{ d: 4, c: 3 }, { b: 2, a: 1 }],
    y: { w: 20, v: 10 },
  };
  const expected = '{"y":{"v":10,"w":20},"z":[{"c":3,"d":4},{"a":1,"b":2}]}';
  assert.equal(stringify(complex), expected);
}

// 3. fast-json-stable-stringify accepts a custom comparator function to customize key ordering
{
  const obj = { a: 1, c: 3, b: 2 };
  // Reverse alphabetical order comparator: receives { key, value } objects
  const reverseCmp = (a, b) => (a.key < b.key ? 1 : -1);
  const result = stringify(obj, { cmp: reverseCmp });
  assert.equal(result, '{"c":3,"b":2,"a":1}');

  // Direct function argument as options
  const directFnResult = stringify(obj, (a, b) => (a.key < b.key ? 1 : -1));
  assert.equal(directFnResult, '{"c":3,"b":2,"a":1}');
}

// 4. fast-json-stable-stringify calls toJSON methods on objects before serialization
{
  const objWithToJSON = {
    name: 'sample',
    nested: {
      toJSON() {
        return { custom: 'serialized', raw: true };
      },
    },
  };
  assert.equal(stringify(objWithToJSON), '{"name":"sample","nested":{"custom":"serialized","raw":true}}');
}

// 5. fast-json-stable-stringify omits undefined object properties and serializes undefined array items or non-finite numbers as null
{
  const obj = {
    a: 1,
    b: undefined,
    c: () => {},
    d: [1, undefined, () => {}, NaN, Infinity, -Infinity],
  };
  assert.equal(stringify(obj), '{"a":1,"d":[1,null,null,null,null,null]}');
}

// 6. fast-json-stable-stringify throws TypeError on circular structures by default and serializes them as cycle placeholders when cycles option is enabled
{
  const circular = { a: 1 };
  circular.self = circular;

  assert.throws(
    () => stringify(circular),
    (err) => err instanceof TypeError && /Converting circular structure to JSON/.test(err.message),
  );

  const handledCycle = stringify(circular, { cycles: true });
  assert.equal(handledCycle, '{"a":1,"self":"__cycle__"}');
}

// 7. fast-json-stable-stringify returns undefined for top-level undefined or function values
{
  assert.equal(stringify(undefined), undefined);
  assert.equal(stringify(() => {}), undefined);
}